Thick film printed circuit

ABSTRACT

A thick film printed circuit in which a plurality of electrode patterns are disposed with approximately equal spaced intervals between one another, resistance patterns having approximately equal widths are mounted between adjacent electrode patterns of said plurality of electrode patterns, and an identical shaped resistance pattern to said resistance pattern is provided so as to align in parallel with at least one of said resistance patterns, whereby exact divided potential can be obtained.

BACKGROUND OF THE INVENTION

The present invention relates to a thick film printed circuit formed ona ceramic substrate or a printing substrate by printing techniques, andmore particularly, relates to a thick film printed circuit for dividingpotentials.

Most thick film printed circuits have the advantage that relativelyexact resistance values can be obtained because the resistance patternsand/or electrode patterns are formed by a printing operation whichordinarily results in rather high precision.

However, where it is desired to produce a voltage divider on a thickfilm circuit by dividing a certain voltage from a resistance of apredetermined fixed value formed by printing, the output voltagesactually obtained often do not meet those theoretically predicted forthe circuit.

SUMMARY OF THE INVENTION

It is the primary object of the present invention to provide a thickfilm printed circuit including a potential dividing circuit by which anydesired divided potentials can be obtained accurately.

It is other object of the present invention to provide a thick filmprinted circuit including a potential dividing circuit which providesuniformity for the divided potentials.

It is further other object of the present invention to provide anexcellent structure of a potential dividing circuit having highperformance which can be constructed by almost the same printingprocesses as those practiced conventionally.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit view showing a general bias circuit of a transistorcircuit,

FIG. 2 is a plan view showing resistance patterns of a potentialdividing circuit in a conventional thick film printed circuit;

FIG. 3 is a sectional view of printed patterns in a printed circuit; and

FIG. 4 is a plan view of a potential dividing circuit in a thick filmprinted circuit according to the present invention.

PREFERRED EMBODIMENT OF THE INVENTION

Prior to describing an embodiment of the present invention, a potentialdividing circuit of a thick film printed circuit typical of the priorart will be described with reference to FIGS. 1-3.

In general, in order to apply a bias voltage to a transistor, as shownin FIG. 1, potential divided by the two resistors (2) and (3) is appliedto base electrode of the transistor (1), and resistors (4) and (5) areconnected, respectively to the collector electrode and the emitterelectrode of the transistor. The transistor is supplied with electricpower through the resistors (2) and (4), and the other resistors (3) and(5) are grounded respectively.

In the above described circuit, in order to print the resistors (2) and(3), and lead wires (6), (7) and (8) for the resistors (2) and (3) wichare adapted to apply bias voltage to base electrode of transistor (1) ona thick film, as shown in FIG. 2 where the same reference numbersdesignate the same parts shown in FIG. 1, the electrode patterns (6),(7) and (8) are previously printed on a substrate by using conductivepaste to form desired electrode configuration, and in addition theresistance patterns (2) and (3) are formed by printing a paste having aresistive property.

In the above described conventional circuit, the resistance value of theresistance pattern (2) is R₁ and it is to be larger than the resistancevalue R₂ of the resistive pattern (3). The resistance patterns arepreferably formed from the same material and thus the dimensions of therespective resistance patterns must be varied accordingly. Thus, withthe width of the resistance pattern (2) being d₁ and its length beingset to l₁ and the width of resistance pattern (3) being d₂ and itslength l₂, l₁ should be greater than l₂ and d₂ should be greater thand₁.

However, in the conventional construction as mentioned the above, it ishard to form the electrode patterns (6), (7) and (8) consistently withthe predetermined separation distances of l₁ and l₂. Further it islikely that the longitudinal edges of the electrode patterns (6), (7)and (8) may have sloping edge portions (9) formed therewith and whenconductive paste is printed thereover the lengths of the separationdistances between those electrode patterns may vary. The designedresistance values may thus not be obtained.

The sloping edge portion (9) extends outwardly, at the largest, 30μ orso, and this value does not vary very much if the distances l₁ or l₂change and is nearly constant regardlss of their length. Consequently,there are some cases in which they significantly vary the ratio of theresistance values of R₁ and R₂. Also, the widths d₁ and d₂ of theresistance patterns (2) and (3) may be changed by those edge portions(9) produced at the ends of the resistance patterns (2) and (3) when theresistive paste is printed to make the resistance non-uniform. Further,if the value of d₁ differs from that of d₂ (i.e., d₁ ≠d₂), the dividedpotentials differ from each other, which is caused by the abovedescribed phenomenon.

These relations can be represented as the following expressions, wherearea-resistance (resistance value of the resistance pattern per unitarea) is r, dispersion (non-uniformity) of the electrode pattern is Δl,and dispersion of the resistance pattern is Δα, and then resistancevalues R₁ and R₂ of the resistance patterns (2) and (3) are represented:##EQU1## and divided potential V is represented as follows; here E isvoltage of an electric power source. ##EQU2## Accordingly, due to thephenomenon in which edge portions (9) are produced in the electrodepattern (6), (7), (8) and the resistance pattern (2), dispersion(non-uniformity) is occurred in those divided potentials. Further, thecauses of occurring non-uniformity of resistance values vary due tochanges of the lengths l₁ and l₂ of the resistance patterns (2), (3) andthe widths d₁ and d₂ thereof which are varied by side edges (9) producedon the abovementioned patterns.

Next, referring to FIG. 4, we will explain an embodiment of the presentinvention in detail. In FIG. 4 a circuit pattern construction to dividethe electric source voltage by one-third is shown. It is configurated asfollows; that is, electrode patterns (10), (11) and (12) are formed withconductive paste at equi-distance with each other on a substrate, thenequi-width resistance patterns (13), (14) and (15) are formed with apaste having resistive property on the substrate. Further, for obtainingone-third potential of the voltage, between the electrode pattern (11)and (12) two resistance patterns (14) and (15) are disposed.

Since the electrode patterns are located on the substrate withequi-distance, the resistance patterns (13), (14) and (15) are equal inlength, and the widths are also adapted to be equal with one another, sothat all resistance values on the potential dividing circuit are made tobe equal. Consequently, at the electrode pattern (11) an exact potentialdivided to one-third of the voltage of the electric power source can beobtained.

Considering the electrode patterns (10), (11), (12), and the resistancepatterns (13), (14) and the side edges (15), the resistance value of Rof the resistance pattern is represented by the following expression:##EQU3## where, separation distance between the electrode patterns is l,length of side edge is Δl, width of the resistance pattern is d and sizeof the side edge is Δd. As can be clearly understood from the aboveexpression, the resistance value is effected by the side edge, however,since the shape of the resistance patterns (10), (11) and (12) are thesame, the resistance value of each of them is equal to R. Now, forexample, we will hereinafter consider a divided potential V, accordingto the following expression; ##EQU4## As can be clearly seen from theabove result, according to the present invention, a constant dividedpotential value can be obtained. Further, in the case of dividing theelectric source to two-fifths, two resistance patterns are providedbetween the electrode patterns (10) and (11) independently, and betweenthe electrode patterns (11) and (12), three resistance patterns areprovided independently with one another, and further it is preferable tomake those resistance patterns an identical shape.

What is claimed is:
 1. A thick film printed circuit including apotential dividing circuit having a plurality of printed resistancepatterns for dividing voltage; said potential dividing circuitincluding:first, second and third electrode patterns; a first resistancepattern having a uniform width extending transversely across the first,second and third electrode patterns; and a second resistance patternadjacent and in parallel to said first resistance pattern, said secondresistance pattern having a width substantially equal to that of thefirst resistance pattern and extending between said second electrodepattern and only one of said first and third electrode patterns.
 2. Athick film printed circuit according to claim 1, wherein a plurality ofsaid second resistance patterns are provided.